Process belt, method for producing paper or nonwoven and use of a process belt

ABSTRACT

Increasingly higher requirements are imposed on the quality and the speed of the production process during the manufacture of nonwovens. It is therefore an object of the invention to provide a process belt for improved nonwoven manufacture. This object is achieved with a process belt for nonwoven or paper manufacture which comprises a device for electrical charging of the process belt. 
     Such a device makes it possible to influence the deposition of nonwoven material on the belt and also to optimally configure the contact between belt and nonwoven material during nonwoven manufacture. 
     In particular, during the transfer of nonwoven material from one belt to another or another installation part, the electrostatic charge assists by repulsion and attraction reactions between nonwoven material and belt.

The invention relates to a process belt for nonwoven or paper manufacture. Process belts for nonwoven or paper manufacture are used during formation of the nonwoven, consolidation of the nonwoven and during the equipping and processing of the nonwoven.

Nonwoven materials owe their origin to the textile, paper, plastics and leather industry. The continuously increasing demand for nonwoven products creates a challenge for the production of raw materials and machines as well as for producers and processor of nonwoven materials.

A precise definition of the term nonwoven material was specified by the International Organisation for Standardisation (ISO 9092, 1988) and the European Standard's Committee (EN-29092).

The three stages of nonwoven production such as formation of the nonwoven, consolidation of the nonwoven and equipping and processing of the nonwoven are either carried out individually or in a continuous process. The production of nonwoven materials begins with the surface or bulk arrangement of the fibres. Depending on wet or dry technology, these can either consist of staple fibres (packed in bales or sacks) or of filaments (spun or molten polymer granules).

In principle, six different processes are used to produce a fibre web for forming a nonwoven: wet nonwoven process, air stream nonwoven process, dry nonwoven process, spunbond nonwoven process, hot air melting process and combi-process.

In the spunbond nonwoven process, PES belts, double-layered with woven-on pin seam and edge coating, PES belts, single-layered with woven seam and edge coating, bronze belts, smooth with endless soldered seam and half-twisted cast steel belts with soldered seam and edge welding are used for forming the nonwoven. Particularly half-twisted VA belts with soldered seam and edge welding are suitable for drying.

In the air stream process, the following belts are preferably used for forming the nonwoven: PES belts, smooth binding, or 2/1 body, preferably open, with endless woven seam and edge coating as well as half-twisted or smooth VA belts, preferably open, with soldered seam and edge welding. In particular, half-twisted VA belts with soldered seam and edge welding are suitable for the fixing and in particular half-twisted VA belts, triple-chain with soldered seam and edge welding, are suitable for drying.

In the dry nonwoven method in particular PTFE-coated gauze fabric with pin seam and adhesive-seam-reinforced edges and duofil belts with flat pin seam and edge coating are used for forming the nonwoven. PTFE-coated gauze fabric with pin seam and edge coating, duofil belts with flat pin seam and edge coating as well as cam belts with pin seam and edge coating are used as part of the drying.

The hot air melting process is frequently combined with a spunbond process. A distinction is made here between two-layer meltblown processes and three-layer combi-processes. In this case, the final consolidation takes place over a dryer belt in the hot-air furnace and also by circulation over a hot air drum or over a calender roller. Particularly PES belts, double-layered with woven-on pin seam and edge coating, PES belts, single-layered with woven seam and edge coating, bronze belts, smooth with endless soldered seam and half-twisted cast steel belts with soldered seam and edge welding are suitable as process belts for forming the nonwoven. Preferably half-twisted VA belts with soldered seam and edge welding are used for drying.

All these methods for nonwoven formation, consolidation and equipment and processing run on special process belts. In this case, high requirements are imposed on the depositing behaviour and the alignment of the fibres.

It is therefore the object of the invention to improve the treatment of nonwoven materials on process belts.

This object is achieved with a process belt for nonwoven and paper manufacture which comprises an electrical device for electrical charging of the process belt.

Process belts are conventionally either earthed through the mechanical arrangement or they receive a special uncontrolled charge due to their construction and their operation. In both cases, the charge of the process belt acts on the process of nonwoven production. This charge can be tolerated as an additional technical disadvantage of the installation. However, the invention is based on the finding that the electrical charge of the process belt can be specifically influenced in order to thereby influence the process of nonwoven production.

The device for electrical charging of a process belt can consist of measurement and regulation of the system-induced electrical charging of the belt. Alternatively or cumulatively, the process belt can be actively electrically charged such as is desired for the nonwoven production process. In this case, a control or regulation is naturally advantageous.

In order to charge a process belt cost-effectively, it is proposed that the device has a slider. Depending on the configuration of the slider, the process belt can thus be charged over its entire width, in special areas transverse to the extension of the belt or in special areas longitudinal to the extension of the belt.

Alternatively or cumulatively it can be provided that the device has a conductive roller or conductive ring. As a result, the process belt can be charged locally or over its entire width.

Noncontact charging of a process belt is achieved with a device which comprises induction means. With this induction means, a charge can be produced locally at positions on the process belt or in the entire process belt according to predefined requirements.

The noncontact charging of the process belt can also take place with the aid of corona charging or by means of ionisation rods.

It is further proposed that the device comprises means for specifically inducing tribo-electric charge. As a result, natural charging processes can be promoted or guided in such a manner that the charge is present in the desired form at the desired location. The use of tribo-electric charging is promoted by the moving belts and the contact and separation of materials such as roller, belt and nonwoven. By means of a specific choice of materials, an electrical charging process which promotes nonwoven production can be achieved by the contact and separation of two materials.

Good results were achieved with process belts comprising a metal. Metal belts promote the distribution of the charge on the surface of the belt.

However, it can also be advantageous if the process belt comprises a conductive plastic. Plastic is particularly suited to holding electrical charges and producing them by means of a tribo-electric effect.

It is therefore further proposed that the process belt has a metal part and a plastic part. The metal part can in particular be provided in the form of wires and/or cables whilst the plastic part is provided in particular in the form of monofil fibres and/or multifil fibres. Specifically this combination of materials leads to a favourable behaviour in regard to the electrical charging.

In order to reduce the tracking forces of the process material on the belt, it is proposed that a charge having the same polarity as the process material is present in the belt. The belt therefore has the same charge as the process material, since like charges repel, this has the result that these repulsion forces can, for example, counteract the weight forces of the process material. When the process material is placed above the belt, this can reduce the tracking forces of the process material and in extreme cases, even lead to a slight suspension of the process material above the process belt. The reduction of the tracking forces can also promote the alignment of the fibres.

Alternatively to same-polarity charging or in other regions of the belt, a charge having the opposite polarity to the process material can be present in the belt. This has the result that in the regions of charge having the opposite polarity to the process material on the belt, the process material is attracted to the belt. This in turn can promote a consolidation of the process material and can prevent the process material from hovering in dust form as thin fibres in space and not reaching the belt. The opposite-polarity charge also makes it possible to charge the belt in the area of the deflecting roller or even on the underside of the belt since it is no longer necessary for the process material to fall onto the belt due to its weight force. As a result, the belt can also be arranged in a position deviating from the horizontal position.

A simple configuration of a process belt provides that the device comprises a direct current source. This direct current source can be used for charging the belt and is preferably used at that point where special charging of the belt is required.

In particular for heating the belt, it is proposed that the device comprises an alternating current source.

Experiments have shown that it is particularly advantageous if the charge is produced specifically in the depositing area of the process material. This improves the depositing in the forming area and therefore accelerates the nonwoven formation.

Another area of application of the electrical charging of the process belts is at the transfer zone. It is therefore proposed that the charge is produced specifically in a transfer zone to another belt or another installation part. Here the transfer can be significantly improved by electrostatic attraction and repulsion forces.

In order to produce locally different charges, it is proposed that only a functional part of the process belt is charged. Thus, for example, it is proposed that only all or only special wefts are electrically charged. On the other hand, only special warps such as, for example, the warps at the edge of the process belt can be electrically charged in order to particularly influence the nonwoven formation in these areas.

The object of the invention is also achieved by a method for producing paper or nonwoven, wherein a process belt, in particular according to the aforesaid explanations, is specifically electrically charged.

In addition, the object is achieved by using such a process belt for carrying out a process with complete or local electrical charging of the process belt.

Exemplary embodiments of the process belt according to the invention vary according to use of the belt during formation of the nonwoven, consolidation of the nonwoven or equipping and processing of the nonwoven. In this case, at least one process belt is electrically charged completely or only locally according to predefined requirements so that an improvement in the nonwoven production is achieved due to the electrostatic forces.

In this case, various belts of different materials can be used and the electrical charge can be applied to the belt material inductively by tribo-electric effects or by sliding contacts. 

1. A process belt for nonwoven or paper manufacture, by comprising a device for electrical charging of the process belt.
 2. The process belt according to claim 1, wherein the device has a slider.
 3. The process belt according to claim 1, wherein the device has a conductive roller or conductive ring.
 4. The process belt according to claim 1, wherein the device has induction means.
 5. The process belt according to claim 1, wherein the device has means for specifically inducing tribo-electric charge.
 6. The process belt according to claim 1, wherein the process belt comprises a metal.
 7. The process belt according to claim 1, wherein the process belt comprises a conductive plastic.
 8. The process belt according to claim 1, wherein the process belt comprises a metal part and a plastic part.
 9. The process belt according to claim 1, wherein a charge having the same polarity as the process material is present in the belt.
 10. The process belt according to claim 1, wherein a charge having opposite polarity to the process material is present in the belt.
 11. The process belt according to claim 1, wherein the device comprises a direct current source.
 12. The process belt according to claim 1, wherein the device comprises an alternating current source.
 13. The process belt according to claim 1, wherein the charge is produced specifically in the depositing area of the process material.
 14. The process belt according to claim 1 wherein the charge is produced specifically in a transfer area to another belt or another installation part.
 15. The process belt according to claim 1, wherein only one functional part of the process belt is charged.
 16. A method for producing paper or nonwoven, wherein a process belt according to claim 1 is specifically electrically charged.
 17. Use of a process belt, in particular a process belt according to claim 1 and specifically with complete or local electrical charging of the process belt. 